When President Bush nominated Michael Mukasey to be attorney general, presidential candidates offered reactions that broke down mostly on party lines -- Republicans positive, Democrats guarded. Rudy Giuliani, whose campaign counts Mukasey as an adviser, gushed that "he will meet and exceed all expectations." John Edwards was a harder sell. "We need to hear more about how Judge Mukasey will repair the serious damage caused by his predecessors," he said.

But what the candidates have to say about the person Bush chose doesn't really matter much. They aren't likely to determine his fate, and even if he's confirmed, Mukasey won't be around long. What would be much more valuable is to know, if they are ever in a position to nominate someone for attorney general, who it would be. You think you could do better? Fine -- take your best shot, right now.

That information might help voters make up their minds. After all, nobody guessed in advance that Bush, upon being elected in 2000, would turn the Justice Department over to a Missouri senator who needed a job, having just lost an election to an opponent who happened to be dead. John Ashcroft was on nobody's list of legal heavyweights. Nor did we know that shortly after being re-elected, the president would give the job to Alberto Gonzales, another nominee whose virtues were far more visible to Bush than to anyone else.

It's good to know what the candidates think about Mukasey and his predecessor at the Justice Department, mainly because those opinions give us an idea what sort of attorney general they envision. Better still, though, for them to give us an idea what sort of attorney general they envision by providing some names.

That shouldn't be too hard for them to do, since most of them are well-connected members of the bar. Rudy Giuliani was associate attorney general under President Reagan, so he knows what the job entails. Fred Thompson was a federal prosecutor and counsel to some important congressional committees.

Barack Obama is a member of the faculty at the University of Chicago law school, where he could find a possible candidate or two. John Edwards was one of the most successful plaintiff's lawyers in America until he went into politics. Joe Biden has been chairman of the Senate Judiciary Committee, which handles the confirmation hearings for each attorney general nominee. Hillary Clinton practiced law back in Arkansas and, during her White House years, got to know several prosecutors, notably Kenneth Starr.

In Britain, the opposition party maintains a "shadow Cabinet" of parliamentarians who are responsible for formulating policy for each government department, and the shadow minister may become the actual minister if the party gains power. So citizens have a pretty good idea what to expect when they vote in the Tories or the Labourites.

But on this side of the Atlantic, we can only guess what lies in store. It's like buying real estate online. You may think you can trust the seller, but ultimately it's up to him whether your property sits on a beach or a toxic waste dump.

In the case of the attorney general, the surprises are rarely pleasant ones. Bill Clinton chose Janet Reno, an obscure local prosecutor, only after his first two choices, Kimba Wood and Zoe Baird, went down in flames. Ronald Reagan gave the job to William French Smith, a pal who had been his personal lawyer. Richard Nixon chose his campaign manager, John Mitchell, who became the first attorney general ever to go to prison. John F. Kennedy picked his younger brother.

This last nomination is one of the few that look better now than they did at first. Anticipating criticism, JFK joked about how he would make the announcement: "I'll open the front door of the Georgetown house some morning about 2:00 a.m., look up and down the street, and, if there's no one there, I'll whisper, 'It's Bobby.' "

Given the dismal experience with Gonzales, it's especially important for the next president to choose someone with sterling credentials, a commitment to excellence and independent judgment. That may be what the candidates expect from Bush's attorney general. But when it comes to picking their own, history suggests, they may set the bar slightly lower. If so, we ought to know now.